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nanrod (Member Profile)

Teenager wins $400,000 for video explaining Relativity

Aziraphale says...

I've seen a video from sixty symbols with a similar explanation (kind of). Does this have any relevance?
https://www.youtube.com/watch?v=Cxqjyl74iu4

dannym3141 said:

This is an excellent explanation for someone of his age and his skill with video editing obviously helps a lot. It held my interest, the world needs more entertaining and educating videos like these.

My only criticism - and some youtubers have already pointed this out - is that the explanation of time dilation "..the same bodily change that happens on earth takes much longer to occur when you are moving so fast.." is wrong.

Signals sent within the body can be analogous to a clock - any fixed duration measured between two ~lightspeed reference frames will be different, including seconds measured by an atomic clock - but time dilation specifically has nothing to do with the mechanics behind how you measure the time or the time it takes a signal to travel. It's a property of the nature of spacetime. Time itself actually slows down. There's no 'trick' to understanding how or why, it's just a property that it has. We can forgive him because he'd already demonstrated that physics is the same in any inertial reference frame and there is no "preferential" reference frame; therefore the motion of the reference frame can't be responsible for the observed difference, so he obviously already really knew all this.

There's no shame in getting that wrong, because he'll be taught more and better about it as he progresses through school. Generally the arbitrary subjects are the hardest to live with because you just have to accept them as they are rather than 'understand'. Quantum mechanics is the same - you just have to accept the rules and apply the maths. Everyone struggles with it, even Feynman said "If you think you understand quantum mechanics, you don't understand quantum mechanics."

Professor Poliakoff Is Knighted! - Periodic Table of Videos

RFlagg (Member Profile)

Science YouTubers - Sixty Symbols

siftbot says...

Tags for this video have been changed from 'sixty symbols, vihart, cgpgrey, smarter every day, Minute Physics' to 'sixty symbols, vihart, cgpgrey, smarter every day, Minute Physics, vi hart' - edited by messenger

The Helical Model

RFlagg says...

Yeah, it struck me as pretty, but I was under the impression that the orbital plane was pretty close to the galactic plane so it would look more like the first model they showed, just adding that the sun itself was orbiting another object... Sort of like if you wanted to watch the moon in an animation like this you wouldn't show the Earth and the moon looking like a comet, but trace the Earth's orbit and show the moon's orbit around the sun. The orbital plane and galactic planes may not line up exactly but close enough I would think to offset the model presented in the video. Pretty though.
How galaxies get their spiral pattern: http://videosift.com/video/Spiral-Galaxies-Sixty-Symbols

Guinness Science - Sixty Symbols

siftbot says...

Tags for this video have been changed from 'sixty symbols, guinness, science, beer, ale, carbonation, nitrogen, widget, 60' to 'sixty symbols, guinness, science, beer, ale, carbonation, nitrogen, widget, 60, physics' - edited by messenger

kulpims (Member Profile)

Zifnab (Member Profile)

messenger (Member Profile)

RFlagg (Member Profile)

eric3579 (Member Profile)

Momentum, Magnets & Metal Balls - Sixty Symbols

messenger says...

Yep, I think you're right. My prediction above could only happen with initial speeds massive enough for the outgoing particle to overcome the magnetic pull, or with the magnet fixed to a spot on the track.

My next question is about why in this video the incoming ball hits twice. In a cradle, it only hits once, and all force is transmitted through the chain of balls in a single pulse, ejecting just one ball. Why should it be different with a magnet? Arguably, it should stick even stronger if there's a force holding it there. Maybe the difference is that in this video the ball is accelerating as it strikes, whereas in the cradle, as the ball's direction approaches level, it's acceleration goes down to zero, so that the moment of impact, there's zero acceleration happening.

An experiment to test this: get a track with a steady slope, and several balls. Hold a group of balls around the middle of the track, and a single ball well above them. Release the single ball towards the group, and before it strikes the group, release the group. The single ball will be accelerating relative to the group and eventually strike it. We can see how many balls are ejected out the front of the group. If more than one, then it's confirmed. If only one, then it's disconfirmed, and probably has something to do with magnetic attraction specifically.>> ^oritteropo:

Momentum can be conserved in a number of ways, and my thought was that if the ball is really stuck to that magnet then rather than ejecting the ball on the other side, the whole lot might just move along the track together. If you've ever played with neodymium magnets you'll know why I think that, the amount of effort required to unstick something from them is surprisingly large.
[minor edit]

Momentum, Magnets & Metal Balls - Sixty Symbols

oritteropo says...

Momentum can be conserved in a number of ways, and my thought was that if the ball is really stuck to that magnet then rather than ejecting the ball on the other side, the whole lot might just move along the track together. If you've ever played with neodymium magnets you'll know why I think that, the amount of effort required to unstick something from them is surprisingly large.
>> ^messenger:

I think ideally, as momentum must be conserved, that the ball would come in, the other ball would be ejected, and decelerated until it escaped the magnetic pull going the same speed as the incoming ball was before it started accelerating.
On a real physical track like this with friction and sound energy loss, I think the ball would be ejected, not overcome the pull of the magnet, and get sucked back pretty quick. It may strike hard enough to send the other ball out a bit, but after very few iterations, they would be all stuck together.
I haven't thought yet about the effect of the magnet moving towards the first ball as it approaches. Maybe this has no net effect at all.


Momentum, Magnets & Metal Balls - Sixty Symbols

messenger says...

I think ideally, as momentum must be conserved, that the ball would come in, the other ball would be ejected, and decelerated until it escaped the magnetic pull going the same speed as the incoming ball was before it started accelerating.

On a real physical track like this with friction and sound energy loss, I think the ball would be ejected, not overcome the pull of the magnet, and get sucked back pretty quick. It may strike hard enough to send the other ball out a bit, but after very few iterations, they would be all stuck together.

I haven't thought yet about the effect of the magnet moving towards the first ball as it approaches. Maybe this has no net effect at all.>> ^oritteropo:

Well it's only a guess, since I'm too lazy to do the calculations , but I don't think the kinetic energy from the impact would be sufficient to overcome the very large magnetic force, so click and no ball ejected.
>> ^messenger:
[...] Now I want to know what would happen if there was only one ball after the magnet. What do you think?




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